The disclosed embodiments of the present invention relate to driving a speaker, and more particularly, to a control device for driving a multi-function speaker by using a digital mixing scheme and related control method thereof.
The conventional multi-function speaker includes “2-in-1 Speaker” and “3-in-1 Speaker”. The functions supported by the multi-function speaker may include audio playback, voice playback, and vibration. Due to its low cost and compact size, the multi-function speaker is widely used in modern communications appliances.
Please refer to FIG. 1, which is a block diagram illustrating a traditional control device for driving a conventional vibration speaker. The vibration speaker 101 shown in FIG. 1 is also called a “2-in-1 speaker”, which is a kind of multi-function speaker that only supports two functions, including audio playback and vibration. The control device 100 employs an analog mixing scheme to mix two analog signal sources with different frequencies (one is for audio playback, and the other is for vibration), and uses the mixed signal to drive the vibration speaker 101. For example, the audio signal may be in a frequency band of 200 Hz-20 kHz, and the vibration signal may be a sinusoidal signal in a frequency band of 100 Hz-200 Hz.
The circuit elements included in the control device 100 are analog devices. That is, an analog high-pass filter (HPF) 114, an analog mixer 116, and an analog amplifier (Amp) 118 are used. As shown in FIG. 1, the audio signal needs to pass through the high order high-pass filter (HPF) 114 in order to remove the low-frequency components included therein. However, the high order high-pass filter (HPF) 114 realized in the analog domain comes with a high cost and cannot be dynamically turned on/off, resulting in degradation in low-frequency performance for the audio signal. Moreover, the audio signal may suffer from signal quality degradation due to passing through the analog mixer 116, resulting in noise and nonlinear distortion present in the filtered audio signal.
As for the vibration signal, most systems in the communications appliances are not equipped with an internal signal source for providing the desired vibration signal, thus requiring an extra processor (e.g., baseband processor) to create a periodical pulse width modulation (PWM) signal to generate such a signal, and also requiring an extra low-pass filter (LPF) 112 to remove the high-frequency components. This inevitably increases hardware costs. In addition, regarding mass production, multi-function speakers often possess vibration point variation during the manufacturing process, which may lead to inconsistent vibrations.
Thus, there is a need for an innovative control device to improve the overall performance of a multi-function speaker.